sqldb: add blinded path tables

This commit adds two new tables: blinded_paths and blinded_path_hops. A
single invoice can have multiple blinded_path entries and a single
blinded_path can have multiple blinded_paths.
The commit also adds various queries for the two new tables.

sqldb/sqlc/migrations/000005_invoice_blinded_paths.down.sql

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+DROP TABLE IF EXISTS blinded_paths;
+DROP TABLE IF EXISTS blinded_path_hops;

sqldb/sqlc/migrations/000005_invoice_blinded_paths.up.sql

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+-- blinded_paths contains information about blinded paths included in the
+-- associated invoice.
+CREATE TABLE IF NOT EXISTS blinded_paths(
+    -- The id of the blinded path
+    id BIGINT PRIMARY KEY,
+
+    -- invoice_id is the reference to the invoice this blinded_path was created
+    -- for.
+    invoice_id BIGINT NOT NULL REFERENCES invoices(id) ON DELETE CASCADE,
+
+    -- last_ephemeral_pub is the public key of the last ephemeral blinding
+    -- point of this path.
+    last_ephemeral_pub BYTEA NOT NULL UNIQUE,
+
+    -- session_key is the private key used for the first ephemeral blinding
+    -- key of this path.
+    session_key BYTEA NOT NULL,
+
+    -- introduction_node is the public key of the first hop of the path.
+    introduction_node BYTEA NOT NULL,
+
+    -- amount_msat is the total amount in millisatoshis expected to be
+    -- forwarded along this path.
+    amount_msat BIGINT NOT NULL
+);
+
+-- blinded_paths_hops holds information about a specific hop of a blinded path in
+-- blinded_paths.
+CREATE TABLE IF NOT EXISTS blinded_path_hops(
+    -- blinded_path_id is the reference to the blinded_path_id this
+    -- blinded_path_hop is part of.
+    blinded_path_id BIGINT NOT NULL REFERENCES blinded_paths(id) ON DELETE CASCADE,
+
+    -- hop_index is the index of this hop along the associated blinded path.
+    hop_index BIGINT NOT NULL,
+
+    -- channel_id is the ID of the channel that connects this hop to the previous one.
+    channel_id BIGINT NOT NULL,
+
+    -- node_pub_key is the public key of the node of this hop
+    node_pub_key BYTEA NOT NULL,
+
+    -- amount_to_fwd is the amount that this hop was instructed to forward.
+    amount_to_fwd BIGINT NOT NULL,
+
+    -- The hop_index is unique per path.
+    UNIQUE (blinded_path_id, hop_index)
+);
+
+CREATE INDEX IF NOT EXISTS blinded_path_hops_path_id_idx ON blinded_path_hops(blinded_path_id);

sqldb/sqlc/queries/blinded_paths.sql

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+-- name: InsertBlindedPath :one
+INSERT INTO blinded_paths (
+    invoice_id, last_ephemeral_pub, session_key, introduction_node,
+    amount_msat
+) VALUES (
+    $1, $2, $3, $4, $5
+) RETURNING id;
+
+-- name: FetchBlindedPaths :many
+SELECT *
+FROM blinded_paths
+WHERE invoice_id = $1;
+
+-- name: InsertBlindedPathHop :exec
+INSERT INTO blinded_path_hops (
+    blinded_path_id, hop_index, channel_id, node_pub_key,
+    amount_to_fwd
+) VALUES (
+    $1, $2, $3, $4, $5
+);
+
+-- name: FetchBlindedPathHops :many
+SELECT *
+FROM blinded_path_hops
+WHERE blinded_path_id = $1
+ORDER BY hop_index;